The present invention relates to a gas scrubber, particularly for the flue gases from heating plants, this scrubber having a processing area through which the gases pass and in this a rotating disc arrangement that rotates about a vertical axis and is installed as a spray system, it being possible to coat this disc arrangement, preferably through a hollow shaft that bears the discs, with a scrubbing agent that is to be sprayed, with the formation of a layer of liquid that adheres to the disc arrangement and is separated from it by the effects of centrifugal force, moving outwards in so doing so as to form an annular spray zone.
A device of this kind is described in German disclosure No. 31 22 026. The particular advantage of this system lies in the fact that spray nozzles--which in other circumstances are always prone to blockage--are not required in this particular system. The scrubbing agent that is to be sprayed is, on the contrary, flung off the disc arrangement, that rotates comparatively fast, at such a speed that very fine droplets of liquid are formed.
However, the construction and design costs of the scrubber described in German Pat. No. 31 22 026 are relatively high since it has to have a special blower in order to maintain the flow of gas that is to be scrubbed through the processing area and at the same time to contribute to the atomisation of the droplets of liquid by the formation of vortices.
For this reason it is the task of the invention to create a gas scrubber that is distinguished by very low construction costs and good fogging of the scrubbing agent and thus very good scrubbing efficiency.
This task has been solved in that the disc arrangement has one or a plurality of preferably perforated discs, these having recesses or aerodynamically effective elements arranged around its periphery, preferably in that the discs are cut repeatedly inwards from the periphery, the blades formed by these cuts being twisted or bent against the plane of the disc or the direction of rotation, respectively, in the manner of propellor blades, at a pitch angle that is such that the gas is displaced radially outwards during rotation, and at the same time in the axial direction of the disc arrangement--preferably downwards against a bath that contains the scrubbing agent--away from the gas inlet area of the processing area.
According to the present invention provision is made such that the same elements that serve to spray the scrubbing agent also serve to move the gas that is to be scrubbed through the processing area. This also causes intensive agitation of both the gas that is to be scrubbed and the scrubbing agent. For the remainder, the perforations or the aero dynamic elements, respectively, as well as the propeller blades form, in each case, separation edges, on which the film of liquid that adheres to the discs separates most effectively during spraying.
The preferred blades are twisted so as to resemble propellor blades, and the perforations themselves, can be produced with the simplest tools.
In an efficient development of the present invention provision can be made such that the disc arrangement is arranged within an annular, preferably stationary cowl, this surrounding the disc arrangement at a radial distance in the direction of rotation, and such that in a disc arrangement incorporating several discs that can be coated with the scrubbing agent the radial distance between the cowl and the edge of the disc is greater in the case of the disc that is furthest removed from the gas input area than is the case of the preceding disc. The cowl forms an impact surface that is constantly wetted by the scrubbing agent and the solids that are carried by the gas that is to be scrubbed impinge on this impact surface and these are then wetted by the scrubbing agent and carried off. The distance between the cowl and the disc, that increases in the direction of flow of the gas that is to be scrubbed contributes to a high throughout of the processing area, in that any "blockage" of the processing area with sprayed or atomised scrubbing agent is counteracted. In this arrangement an increasing cross-section is available to the quantity of the sprayed scrubbing agent, which increases in the direction of flow of the gas that is to be scrubbed.
Furthermore, it is foreseen that the hollow shaft is only supported in the area of its upper extremity, preferably in that the hollow shaft is connected, without its own bearings, directly to the shaft of a motor that is used to drive the disc arrangement, and is supported radially and axially exclusively by means of the motor shaft bearings, and also that the open lower extremity of the hollow shaft is immersed in the bath that contains the scrubbing agent and that by means of the propellor like delivery blades arranged in the open extremity, liquid is picked up from the bath when they rotate, is drawn into the hollow shaft and moved to openings that are arranged in the walls of the hollow shaft, in each instance close to or on the plane of the disc.
In order to use the heat contained in the gas that is to be scrubbed, these gases--preferably prior to their introduction into the processing area--can be passed through a heat exchanger, this being most expediently arranged in such a manner that the condensate that forms on it can drip into the bath, e.g., in that the heat exchanger is arranged within an annular space that surrounds the processing area, the said annular space being delimited below by the surface of the bath. This arrangement is characterized in that the heat that is given off by the heat exchanger is relatively high and the large quantities of heat that are given off on condensation of the contaminants that are in the form of vapour can be utilised simultaneously. The heat exchanger also works as a pre-scrubber, since some of the contaminants are removed from the gas that is to be scrubbed when the steam condenses, before it enters the processing area.
If necessary, additional gas--preferably additional air if flue gases are to be scrubbed--can be introduced into the gas that is to be scrubbed, and a neutralising agent--preferably soda (sodium carbonate) if flue gases are to be scrubbed and water is to be used as the scrubbing agent--can be added to the bath.
In this way, if flue gases are involved, the sulfur dioxide that is contained in the gas can be trapped by the formation of sodium sulfate The sodium carbonate (soda) and the water together form hydrosodic carbonate with the carbon dioxide that is contained in the flue gas and this is converted to sodium sulfate with the oxygen that is contained in the additional air and with the sulfur dioxide that is contained in the flue gas although carbonic acid may be formed at the same time, this, however, decomposes for the most part into carbon dioxide and water.
The bath can be configured as a sedimentation basin, the hollow shaft with its lower, open extremity and the delivery blades that are immersed in the bath being arranged, if necessary, above a baffle plate that is arranged in the bath so as to prevent any agitation of the precipitated solids. The sludge that collects on the bottom of the bath can be moved into a drying container, this preferably being arranged in the gas line that leads to the gas scrubber, particularly if warm or hot gases, such as flue gas, are to be scrubbed.
In order to manage without costly and temperamental sludge pumps, it is possible to produce a partial vacuum within the closed drying container by means of an evacuation system so that the sludge can be moved into the drying container through a suction line that passes from the bottom of the sedimentation basin into the elevated drying container. At the outlet end, the evacuation system opens preferably into the feed line for the gas scrubber for the gas that is to be scrubbed, or into the bath.
The present invention will be described below on the basis of a preferred exemplary version that is illustrated in the drawings appended hereto.